The present invention relates generally to radiation therapy and strategies for programming a radiation therapy machine. More particularly the invention relates to a system for determining a radiation treatment plan, a corresponding method and a radiation therapy machine. The invention also relates to a computer program product, a computer readable medium and a radiation therapy method.
Radiation therapy may be employed to treat tumorous tissue. In radiation therapy, a high energy beam of radiation is aimed towards a patient. More precisely, a radiation source produces a beam of radiation that is collimated and directed into a target volume in the patient. The dose and placement of the dose must be accurately controlled to, on one hand, ensure that the tumor receives sufficient radiation; and, on the other hand, that damage to the surrounding healthy tissue is minimized. Before performing the radiation therapy, a radiation treatment plan is determined in a radiation planning session. This allows an accurate and precise dosage of radiation to be delivered to the patient.
WO 2010/025115 describes a method for determining a radiation treatment plan including defining treatment control points, defining dose calculation points, calculating dose in the dose calculation points, and changing a number of the dose calculation points. The proposed method for determining a radiation treatment plan includes modeling a first part of a treatment plan using a fluence map, and modeling a second part of the treatment plan using a first machine parameter. The method for determining a radiation treatment plan includes determining a plurality of dose calculation points, determining a level of complexity of fluence for one or more machine parameters for one of the plurality of dose calculation points based on the determined level of complexity.
A fluence map specifies the irradiance through a surface (e.g. a plane) integrated over time. The fluence map may be represented by a matrix, in which each element indicates the amount of radiation that shall pass through a certain sub-region of the surface. In fluence map optimization, an optimization algorithm determines a fluence map by modifying the matrix elements that represent the fluence map. The goal of the optimization is to improve upon an objective function quantifying, for instance the quality of the dose distribution that would result from the fluence map.
An arbitrary fluence map cannot always be delivered by a treatment machine because of the physical limitations of the machine. Typically, therefore, the fluence map is converted into a control-point sequence describing machine settings (e.g. multi-leaf collimator (MLC) leaf positions, jaw positions, dose rate, delivery time, monitor units, gantry angle) that yield a fluence being as close as possible to the fluence defined by the fluence map. Errors introduced in the conversion can be reduced by direct machine-parameter optimization, in which an optimization algorithm modifies the machine settings of the control point sequence in order to improve upon an objective function quantifying, for example the quality of the dose distribution that would result from the control point sequence.